iMac Pro vs HP Z8

We have 3 edit bays with old Grey Tower Mac Pros that are screaming for update. Since Apple kind of let the Pro line drift away we were commited to go PC with the new HP Z8 workstation line. That was until de new iMac Pros were introduced just recently and we suddenly began wondering if we should turn to PC.

We mainly do offline editing to transcoded HD material on a Unity server to later online Camera Raws that are grade at an external grading studio.

Bit we also want to have the ability of making basic color grading on 4k Material directly on AVID or on 3rd Party software.

The iMac is known for its not upgradable configurations, while PCs are very upgradable in all its components. The price Tag was also always an issue, but ro be fair, the new iMacs Pro are very reasonable priced, to the point that the actual price tag for a similar configuration would come to the same ammount of an HP Z8. The iMac Pro has the advantage of the 5K dispaly built in, which for a Workstation would have to me extra. It also comes bundled with 10gb Ethernet and Thunderbolt 3 ports, which would all come at an extra cost on the Z8.

Furthermore, the Z8 just got its fmalimg AVID certification while the iMacs Pro will probalby have to wait a while for it.

We have been waiting for an upgrade since almost over a year, looking if Apple would announce new Mac Pros which will eventually happen, but we cannot really wait any longer as we have multiple projects in the pipeline that need to catered in an efficient manner.

So we´re not really sure what to do now. Should we turn to the upgradable certified HP Powerhouse or commit to the MAC line in which our whole Post department is based? Any thoughts, experience, suggestions or tips?